JP5357845B2 - Polarization mode dispersion stress generation method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate any PMD without the need of complicated control at low cost. <P>SOLUTION: A light signal which is incident to a light incidence part 21 is separated into two cross polarization components by polarized-wave separation means 23, and one of the components is given to first delay means 25 while the other is given to second delay means 26. The cross polarization components delayed by both of the delay means 25 and 26 are multiplexed by polarized-wave multiplexing means 28 to be emitted from a light emitting part 29. At least one of the delay means (the second delay means 26) rotates, by a rotating device 52, a mirror array 51 where a plurality of orthogonal mirrors 50 are integrated to respectively receive and return the polarized and separated light by separating it in the width direction of the light. The delay means then changes and transmits a delay time difference given to the light component respectively returned by each of the orthogonal mirrors 50, and changes a group delay time difference of the polarized components of the light multiplexed by the polarized-wave multiplexing means 28. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

The present invention relates to polarization mode dispersion (PMD: Polarization Mode) of light, which is a problem in high-speed optical communication.
More particularly, the present invention relates to a polarization mode dispersion stress generating apparatus necessary for measuring the proof strength of an optical transmission system, optical components, etc., and more particularly, to a technique for enabling an arbitrary PMD to be set at a low cost.

  Conventionally, a PMD emulator has been used as a device used in a PMD tolerance test for an optical communication system. A PMD stress is applied to light incident on a test object by the PMD emulator, and a bit error rate for an optical signal emitted from the test object. (BER) is measured, and the strength evaluation is performed by associating the magnitude of PMD stress to be applied with BER.

  PMD is defined as a difference in transmission speed between two orthogonal polarizations when an optical signal passes through an optical component. When discussing PMD, it is a certain time at a specific wavelength that actually affects signal degradation. Is a group delay time difference DGD (Differential Group Delay) between the two polarizations in FIG. 2, and PMD is an average value of DGD with respect to wavelength and time.

  PMD is a speed difference between orthogonal polarization components of light, and the following three methods have been proposed so far to generate this.

  In the first method, as disclosed in Patent Document 1, a polarization controller is arranged between a plurality of birefringent elements arranged in series with respect to an optical path, and the polarization of light passing through these polarization controllers is reduced. In this method, PMD is generated by randomly changing a wave and applying DGD to orthogonal polarization components. In this method, by increasing the number of birefringent elements, the distribution of DGD can be made close to the ideal Maxwell distribution, and higher order PMD can be generated.

  However, in this first method, since the amount of DGD is determined by the phase difference given by the birefringent element, it is difficult to give an arbitrary DGD. In addition, it is difficult to generate DGD that changes instantaneously, and moreover, since a plurality of birefringent elements and a polarization controller are required, it is difficult to reduce the size and cost.

  As the second method, as disclosed in Patent Document 2 (particularly FIG. 10), a plurality of birefringent elements arranged in series with respect to the optical path are mechanically rotated, and each birefringent element is used. By changing the phase difference, PMD is generated, and this method can also generate higher-order PMD.

  However, as in the first method, it is difficult to give an arbitrary amount of PMD, and a plurality of birefringent elements and a mechanism for rotating these elements are required, which makes it difficult to reduce the size and cost.

  As a third method, as disclosed in Patent Document 3, the light is separated into orthogonal polarization components, one of the lights is delayed by a variable delay device, and combined with the other light. Thus, PMD (DGD) is generated. This method can generate an arbitrary and accurate DGD corresponding to the delay amount of the variable delay device.

Japanese Patent No. 4098630 JP 2006-086955 A JP 2003-143088 A

  However, the third method cannot generate higher order PMD in principle. In addition, when the DGD is changed with time in the configuration of the third method, it is assumed that the delay amount of the variable delay device is changed by a periodic function (for example, a sine function having a constant amplitude). In this case, the DGD generation distribution is As shown in FIG. 11, a concave distribution with a high probability of occurrence at both ends and a low central portion is obtained, which is far from a convex Maxwell distribution. That is, in order to generate DGD with an occurrence probability close to the Maxwell distribution using a variable delay device, extremely complicated delay amount variable control is required for the variable delay device, which is difficult to realize.

  In view of the above circumstances, an object of the present invention is to provide a polarization mode dispersion stress generation method and apparatus capable of generating an arbitrary PMD at low cost without requiring complicated control.

In order to achieve the above object, a polarization mode dispersion stress generation method according to claim 1 of the present invention comprises:
Separates the optical signal to be given polarization mode dispersion into two orthogonal polarization components,
The separated one orthogonal polarization component is propagated in the first optical path, the other orthogonal polarization component is propagated in the second optical path, and at least one of the first optical path and the second optical path In this optical path, the polarization-separated light is divided in the width direction, and each of the plurality of orthogonal mirrors (50) receives and folds back the optical path to give different delays in the width direction. By rotating integrally with an axis parallel to the boundary line where a pair of orthogonal reflecting surfaces forming an orthogonal mirror intersects, the delay time difference given to the light component folded by each orthogonal mirror is changed and propagated. ,
Light in which the orthogonal polarization components propagated through the first optical path and the second optical path are combined, and the group delay time difference between the orthogonal polarization components changes according to the rotation angles of the plurality of orthogonal mirrors. Is generated.

The polarization mode dispersion stress generator according to claim 2 of the present invention is
A light incident part (21) for causing an optical signal to be given polarization mode dispersion to be incident;
Polarization separation means (22, 23) for separating the optical signal incident on the light incident portion into two orthogonal polarization components;
First delay means (25) for receiving one of the two orthogonally polarized components, passing through the first optical path, and emitting with a delay corresponding to the length of the first optical path;
Second delay means (26) for receiving the other of the two orthogonally polarized components, passing through the second optical path, and emitting with a delay corresponding to the length of the second optical path;
Polarization multiplexing means (22, 28) for combining one orthogonal polarization component delayed by the first delay means and the other orthogonal polarization component delayed by the second delay means;
A light emitting section (29) for emitting the light combined by the polarization multiplexing means to the outside,
At least one of the first delay means and the second delay means is:
A plurality of orthogonal mirrors (50) that receive and fold the polarization-separated light separately in the width direction, and the plurality of orthogonal mirrors are parallel to a boundary line where a pair of orthogonal reflecting surfaces forming the orthogonal mirror intersect. A rotation device (52) that rotates integrally with a shaft, and propagates while varying a delay time difference imparted to each light component folded by each orthogonal mirror, and the polarization multiplexing means The group delay time difference of the polarization components of the combined light is changed according to the rotation angles of the plurality of orthogonal mirrors.

A polarization mode dispersion stress generator according to claim 3 of the present invention is the polarization mode dispersion stress generator according to claim 2,
A single polarization beam splitter (22) serves as both the polarization separation means and the polarization multiplexing means,
Quarter wavelength plates (31, 32) are inserted between the polarization beam splitter and the first delay means and between the polarization beam splitter and the second delay means, respectively.
The first delay means and the second delay means receive the orthogonal polarization components separated by the polarization beam splitter through the quarter wavelength plates, and fold them in the opposite directions around the same optical axis, and again Incident light into a quarter-wave plate, converted into orthogonal polarization components whose polarization directions are 90 degrees different from those at the time of separation, and returned to the polarization beam splitter with the same optical axis as that at the time of separation, The optical beam is emitted along an optical axis orthogonal to an incident optical axis of the optical signal to the polarizing beam splitter.

The polarization mode dispersion stress generator according to claim 4 of the present invention is the polarization mode dispersion stress generator according to claim 2,
The polarization separation means and the polarization multiplexing means are each constituted by individual polarization beam splitters (23, 28).

The polarization mode dispersion stress generator according to claim 5 of the present invention is the polarization mode dispersion stress generator according to any one of claims 2 to 4.
A beam expander (53) for expanding the beam width of light incident on the plurality of orthogonal mirrors is disposed between the polarization separating means and the plurality of orthogonal mirrors.

A polarization mode dispersion stress generator according to claim 6 of the present invention is the polarization mode dispersion stress generator according to any one of claims 2 to 5,
The light incident part is provided with a collimator (21b) that widens the beam width of incident light to make parallel light, and the light emitting part is provided with a condenser lens (29a) for condensing the combined light. And
The collimator of the light incident part and the condensing lens of the light emission part are respectively formed by two sets of cylindrical lenses whose beam width expansion directions are orthogonal to each other.

A polarization mode dispersion stress generator according to claim 7 of the present invention is the polarization mode dispersion stress generator according to any one of claims 2 to 5,
The light incident portion is provided with a polarization scrambler (21c) for randomizing the polarization state of incident light.

A polarization mode dispersion stress generator according to claim 8 of the present invention is the polarization mode dispersion stress generator according to any one of claims 2 to 6,
A branching device (56) for branching a part of the light combined by the polarization multiplexing unit and output to the light output unit;
An analyzer (57) having a polarization axis inclined by 45 degrees with respect to both polarization directions so as to extract both polarization components from the light branched by the splitter;
A light receiver (58) for receiving both polarization components detected by the analyzer;
The light reflection means (25a) included in at least one of the first delay means and the second delay means is slid in a direction parallel to the incident optical axis, and the optical path length turned back by the light reflection means is uniformly changed. Slide driving means (25b)
The first delay means based on the output of the light receiver when the slide driving means is controlled in a state where a broadband light source is incident from the light incident portion and the angles of the plurality of mirrors are fixed to a predetermined angle. And adjusting the optical path lengths of the second delay means, and rotating the plurality of mirrors from the predetermined angle when the optical path lengths are matched.

  As described above, the present invention separates an optical signal to be applied with polarization mode dispersion into two orthogonal polarization components, propagates one orthogonal polarization component in the first optical path, and transmits the other orthogonal polarization component. A wave component is propagated through the second optical path, and at least one of the two optical paths is formed with a folded optical path that divides the polarization-separated light into its width direction and receives it by a plurality of orthogonal mirrors (50). Then, by rotating the plurality of orthogonal mirrors integrally with an axis parallel to the boundary line where the pair of orthogonal reflecting surfaces forming the orthogonal mirrors intersects, the light components respectively given back by the orthogonal mirrors are given. Propagating by changing the delay time difference, and combining the orthogonal polarization components propagated through the first optical path and the second optical path, the group delay time difference between the orthogonal polarization components is the rotation of the plurality of orthogonal mirrors Produces light that changes with angle To have.

  For this reason, arbitrary DGD can be given based on the rotation angles of a plurality of orthogonal mirrors, and when light is incident through a single mode optical fiber, the light intensity emitted from the optical fiber has a Gaussian distribution. DGD having a Gaussian distribution can be generated.

  Further, since the part mechanically driven as the apparatus is only a mechanism for integrally rotating a plurality of orthogonal mirrors, it is possible to reduce the size and cost.

  Further, when the beam expander (53) for expanding the beam width of the light incident on the plurality of orthogonal mirrors is disposed between the polarization separating means and the plurality of orthogonal mirrors, a larger delay time difference can be achieved with a small optical system. Can be granted.

  Further, when the collimator of the light incident part and the condensing lens of the light emission part are respectively formed by two sets of cylindrical lenses whose beam width expansion directions are orthogonal to each other, a larger delay time difference can be given.

  Further, in the case where a polarization scrambler is provided in the light incident part, the polarization dependency of incident light can be eliminated.

Basic configuration diagram of the present invention Explanatory drawing for giving different delay time differences in the width direction to polarization components Configuration diagram of the first embodiment of the present invention Configuration diagram of second embodiment using beam expander The figure which shows the structural example of a beam expander The block diagram of 3rd Embodiment using a cylindrical lens The block diagram of 4th Embodiment which provided the slide drive device 25b in the 1st delay means 25 Configuration diagram of the fifth embodiment in which the polarization separating means and the polarization multiplexing means are configured by independent PBSs. The figure which shows the structural example of 6th Embodiment which provided the polarization scrambler in the light-incidence part. The figure which shows the structural example of 7th Embodiment which provided the return optical path by the mirror array in both the delay means. The figure which shows the example of DGD generation distribution

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a basic configuration diagram of a polarization mode dispersion stress generator 20 according to the present invention.

  In FIG. 1, a light incident part 21 is for making an optical signal Pin (here, linearly polarized light) to be given polarization mode dispersion incident. , A connector for connecting the optical fiber, and a collimator lens that collimates light incident from the connector.

  The optical signal Pin incident on the light incident portion 21 is incident on the polarization separation means 23 and separated into two orthogonal polarization components (P wave and S wave) Pp and Ps. As the polarization separation means 23, a polarization beam splitter is mainly used.

  One of the separated orthogonal polarization components Pp is incident on the first delay means 25, and the other Ps is incident on the second delay means 26. The first delay means 25 and the second delay means 26 receive incident light, pass through the first optical path and the second optical path, respectively, and emit with a delay corresponding to the optical path length.

  However, at least one of the first delay means 25 and the second delay means 26 (second delay means 26 in this figure) gives a delay time difference in the optical path and is controlled so that the delay time difference fluctuates.

  In order to realize this, the second delay means 26 includes a mirror array 51 and a rotating device 52 that rotates the mirror array 51.

  As shown in FIG. 2, the mirror array 51 has a pair of reflecting surfaces 50a and 50b orthogonal to each other, and the light incident on one of the reflecting surfaces is light parallel to the incident optical axis through the other reflecting surface. The orthogonal mirror unit 50 that is folded back and emitted from the shaft is integrally formed in a state where the light Ps from the polarization beam splitting unit 23 is continuously arranged in a plurality of stages within the width dimension. 52, the entire mirror array 51 is rotated around an axis A (axis orthogonal to the paper surface) parallel to the boundary line where the pair of reflecting surfaces that form each orthogonal mirror unit 50 intersect, and light to the mirror array 51 is transmitted. Vary incident angle.

  The second delay means 26 includes a return optical path by the mirror array 51. The second delay means 26 receives the light from the polarization separation means 23 in the width direction and receives it by a plurality of orthogonal mirror units 50 of the mirror array 51, respectively. It will be folded.

  Here, as shown in FIG. 2, assuming that the incident angle of light to the mirror array 51 is θ and the optical path difference between adjacent orthogonal mirror units is d, the optical path difference generated between n orthogonal mirror units is nd = 2 × W × sin θ, and by varying this optical path difference by the rotation device 52, a varying delay time difference is given to each component in the width direction of the folded light Ps ′. The group delay time difference between the polarization components of the light combined by the means 28 can be changed.

  One orthogonal polarization component Pp ′ delayed by the first delay means 25 and the other orthogonal polarization component Ps ′ delayed by the second delay means 26 are orthogonalized by a polarization multiplexing means 28. Combined as a component. The polarization beam combining means 28 is composed of a polarization beam splitter, like the polarization separation means 23.

  The light Pout combined by the polarization multiplexing unit 28 is emitted through the light emitting unit 29. The light emitting section 29 includes an output connector, a condensing lens that converges the light emitted from the polarization multiplexing means 28 as parallel light on the incident section of the connector, and the like.

  The control unit 30 controls the rotation device 52 of the delay means including the mirror array 51 and the rotation device 52, as described above, of the first delay means 25 and the second delay means 26, and has a predetermined initial angle, The mirror array 51 is rotated with the rotation amplitude to change the group delay time difference of the polarization component of the light Pout combined by the polarization multiplexing means 28.

  In the polarization mode dispersion stress generator 20 having such a basic configuration, two orthogonally polarized components Pp and Ps that have undergone polarization separation are made incident on the respective delay means 25 and 26, and at least one of the delay means. Since a delay time difference due to the rotation of the mirror array 51 is given to the width direction component of the light incident on the light beam and combined with the other and emitted, any DGD corresponding to the rotation amount of the mirror array 51 is obtained. (Ie, any PMD as its average value).

  In addition, since the light of at least one polarization component is divided in the width direction to give different delay time differences, compared to a method in which the delay time of one entire polarization component is changed uniformly and sinusoidally. Thus, more complicated delay time fluctuations can be realized, and DGD having a desired distribution (such as Maxwell distribution or Gaussian distribution) can be generated according to the intensity distribution of light incident on the mirror array 51. .

  Furthermore, since the mechanically driven part is only at least one of the delay means 25 and 26, and basically only the mirror array 51 is rotated, the size and cost can be reduced.

(First embodiment)
Next, the first embodiment having a more specific configuration will be described with reference to FIG.
In the polarization mode dispersion stress generating apparatus 20 of FIG. 3, the light incident part 21 includes a connector 21a for making the optical signal Pin incident and a collimator lens 21b for making the incident light parallel light, and the light incident part. The light emitted from 21 is received by a PBS (polarized beam splitter) 22.

  This polarization mode dispersion stress generator 20 has a so-called Michelson interferometer structure in which one PBS 22 serves as both the polarization separation means 23 and the polarization multiplexing means 28 described above. The signal Pin is divided into two orthogonal polarization components Pp and Ps, one of which is incident on the first delay means 25 and the other Ps is incident on the second delay means 26, and the emitted lights Pp ′ and Ps ′ are obtained. It returns to PBS22 and becomes a structure which multiplexes.

  Here, the first delay means 25 is constituted by an orthogonal mirror 25a for folding incident light along an outgoing optical axis that coincides with the incident optical axis. However, since the light reflected by the orthogonal mirror 25a is in the same polarization state as that at the time of incidence, if the folded light is returned to the PBS 22 as it is, it returns to the incident light Pin side due to the reversibility of the PBS 22, and Separation becomes difficult.

  Therefore, a ¼ wavelength plate 31 is provided between the PBS 22 and the first delay means 25. This quarter-wave plate 31 is arranged so that its optical axis is 45 degrees with respect to the polarization direction of the incident light.

  As a result, the polarization component Pp emitted from the PBS 22 becomes circularly polarized light by the quarter wavelength plate 31, is folded by the orthogonal mirror 25a, and is incident on the quarter wavelength plate 31 in the opposite direction again. From the four-wavelength plate 31 to the PBS 22, the polarization component Pp ′ whose polarization direction is rotated by 90 degrees with respect to the original polarization component Pp is emitted. This polarization component Pp ′ re-enters the PBS 22, but it is 90 degrees different from the polarization direction at the time of separation, so it does not return to the incident direction of the optical signal Pin but is emitted in a direction orthogonal to the direction (downward in the figure). The

  Further, as described above, the second delay means 26 includes a mirror array 51 in which the reflecting surfaces of the plurality of orthogonal mirror units 50 are continuously formed on one surface side, and a rotating device that rotates the mirror array 51. 52, and has a structure in which the other polarization component Ps emitted from the PBS is folded back with a delay time difference that varies and varies in the width direction.

  However, also in this case, the polarization state of the light reflected by the mirror unit 51 does not change. Therefore, if the returned light is returned to the PBS as it is, it returns to the incident light Pin side, and the polarization component Ps' Cannot combine.

  Therefore, a quarter-wave plate 32 is also arranged between the PBS 22 and the second delay means 26 as shown. Also in this case, the quarter wavelength plate 32 is arranged so that the optical axis of the quarter wavelength plate 32 is 45 degrees with respect to the polarization direction of the incident light.

  As a result, the polarization component Pp emitted from the PBS 22 becomes circularly polarized light by the quarter wavelength plate 32, is folded back by the mirror array 51, and is incident on the quarter wavelength plate 32 again in the opposite direction. From the four-wavelength plate 32, the polarization component Ps ′ whose polarization direction is rotated by 90 degrees with respect to the original polarization component Ps is emitted from the PBS 22. This polarization component Ps ′ re-enters the PBS 22, but does not return to the incident direction of the optical signal Pin because it is 90 degrees different from the polarization direction at the time of separation, and is emitted in a direction (downward in the figure) perpendicular thereto. The

  The lights Pp ′ and Ps ′ turned back from these delay means are incident on the same position in the direction orthogonal to the PBS 22 again with polarization planes that are 90 degrees different from those at the time of separation. Are combined with the light Pout having the orthogonal components on a common optical axis (downward in the figure) orthogonal to the incident optical axis, and output to the outside through the light emitting unit 29.

  The light emitting unit 29 converges the light combined by the PBS 22 on the output connector 29b by the condenser lens 29a and outputs the light from the connector 29b to the outside.

  The control unit 30 controls the rotation device 52 of one of the two delay units 25 and 26 (in this case, the second delay unit 26) to rotate the mirror array 51 at a preset initial angle and rotation amplitude. The group delay time difference DGD between the orthogonal polarization components of the outgoing light Pout is varied to give a desired occurrence probability distribution.

  In addition, although the 1st delay means 25 of the said embodiment folded the incident light with the orthogonal mirror 25a, you may fold with a plane mirror. The same applies to the embodiments described later.

(Second Embodiment)
In addition, as shown in FIG. 4, a beam expander 53 may be provided at the incident portion of the second delay means 26 to increase the width of the light incident on the mirror array 51. By doing so, a larger delay time difference can be given with a small optical system. The beam expander 53 can be arranged at an arbitrary position between the PBS 22 as the polarization separation means and the mirror array 51.

  The beam expander 53 is a combination of a concave lens 53a and a convex lens 53b as shown in FIG. 5A, or a combination of triangular prisms 53c and 53d as shown in FIG. 5B. Can be used.

(Third embodiment)
In addition, as shown in FIG. 6, the collimator 21b of the light incident portion 21 and the condensing lens 29a of the light exit portion 29 are each made of two sets of cylindrical lenses 21b ′, 21b ″, 29a ′, whose beam width expanding directions are orthogonal to each other. 29 ″ can be used to widen the beam width of light propagating between them in a two-dimensional direction to give a larger delay time difference.

(Fourth embodiment)
Further, in order to vary the delay time on one arm side with respect to the position where the optical path lengths of both arms of the interferometer coincide with each other, as shown in FIG. The emitted light is branched and applied to an analyzer 57 whose polarization axis is inclined by 45 degrees with respect to both polarization directions, and light (light including both polarizations) emitted from the analyzer 57 is incident on a light receiver 58. The intensity is detected and given to the control unit 30. Further, the position of the orthogonal mirror 25a of the first delay means 25 is slid by the slide drive device 25b so that the distance from the PBS 22 can be varied, and the control unit 30 changes the angle of the mirror array 51 of the second delay means 26. In a state of being fixed at a predetermined angle, a broadband light source is incident from the light incident portion 21 and the orthogonal mirror 25a of the first delay means 25 is moved so that the intensity of light incident on the light receiver 58 is maximized (interference). The position where the optical path lengths of both arms of the meter coincide with each other is determined, and the mirror array 51 is rotated from a predetermined angle with reference to this position.

  In this example, the orthogonal mirror 25a as the light reflecting means of the first delay means 25 is slid by the slide drive device 25b, and the optical path length of the first delay means 25 is changed uniformly, but the second delay means 26 is used. The same operation can be obtained by sliding the mirror array 51 in addition to turning.

(Fifth embodiment)
In the first embodiment, the configuration (Michelson interferometer) in which the single PBS 22 serves as the polarization separation means 23 and the polarization multiplexing means 28 is shown. However, as shown in FIG. A so-called Mach-Zehnder interferometer configuration constituted by an independent PBS can also be adopted.

  That is, the light incident from the light incident portion 21 is divided into two orthogonal polarization components Pp and Ps by the PBS 23 as the polarization separation means, and emitted to the first delay means 25 and the second delay means 26, respectively.

  The first delay means 25 receives the incident polarization component Pp by the PBS 61, changes the direction by 90 degrees, and transmits the emitted light through the ¼ wavelength plate 31, turns back by the orthogonal mirror 25a, and ¼ wavelength plate 31. Then, the light enters the PBS 28 as polarization multiplexing means via the PBS 61.

  Further, the second delay means 26 receives the polarization component Ps from the PBS 23 by the PBS 62, passes it, enters the mirror array 51 through the quarter wavelength plate 32, and converts the return light to 1 / The light enters the PBS 28 via the four-wave plate 32 and the PBS 62.

  Here, the four PBSs 23, 61, 62, and 28 are arranged orthogonally so as to form a rectangle. The operation of the quarter-wave plates 31 and 32 is the same as described above for converting the polarization direction.

  As a result, the polarization component Ps incident on the second delay means 26 is given a delay time difference that varies and varies in the width direction in the optical path folded back by the mirror array 51, as described above, and the other polarization component. It is emitted to the PBS 28 together with Pp ′, combined with the light Pout in the same manner as described above, and emitted to the outside through the light emitting portion 29.

(Sixth embodiment)
In each of the above embodiments, the incident optical signal Pin is linearly polarized, and the polarization plane is such that the magnitudes of the two orthogonal polarization components separated by the PBSs 22 and 23 constituting the polarization separation means 22 are substantially equal. However, in each embodiment, as shown in FIG. 9, a polarization scrambler 21c is provided in the light incident part 21, and this is controlled by the control part. 30. By changing the polarization of the incident optical signal Pin at random, the effective amount of delay between the polarization components of the outgoing light Pout can be given without being aware of the polarization direction of the optical signal Pin. Can do.

(Seventh embodiment)
Further, in each of the above embodiments, one of the first delay means 25 and the second delay means 26 (here, the second delay means 26) is provided with a return optical path by the mirror array 51. Thus, both the delay means are provided with the mirror array 51 and the rotation device 52, and both are driven simultaneously (however, at least one of the rotation period, amplitude and phase is different). It is also possible to give more complex fluctuations between the wave components. In this case, the first delay means 25 of the Michelson type shown in FIG. 3 can have the same configuration as the second delay means 26, or can be applied to any of the Mach-Zehnder type shown in FIG.

  DESCRIPTION OF SYMBOLS 20 ... Polarization mode dispersion | distribution stress generator, 21 ... Light incident part, 22 ... Polarization beam splitter (PBS), 23 ... Polarization separation means (PBS), 25 ... First delay means, 25a ... Orthogonal mirror, 25b... Slide drive device, 26 ... second delay means, 28 ... polarization multiplexing means (PBS), 29 ... light emitting section, 30 ... control section, 31, 32 ... 1 / 4 wavelength plate, 50 ... orthogonal mirror unit, 51 ... mirror array, 52 ... rotating device, 53 ... beam expander, 56 ... branching device, 57 ... analyzer, 58 ... light receiver, 61 62 …… PBS

Claims (8)

Separates the optical signal to be given polarization mode dispersion into two orthogonal polarization components,
The separated one orthogonal polarization component is propagated in the first optical path, the other orthogonal polarization component is propagated in the second optical path, and at least one of the first optical path and the second optical path In this optical path, the polarization-separated light is divided in the width direction, and each of the plurality of orthogonal mirrors (50) receives and folds back the optical path to give different delays in the width direction. By rotating integrally with an axis parallel to the boundary line where a pair of orthogonal reflecting surfaces forming an orthogonal mirror intersects, the delay time difference given to the light component folded by each orthogonal mirror is changed and propagated. ,
Light in which the orthogonal polarization components propagated through the first optical path and the second optical path are combined, and the group delay time difference between the orthogonal polarization components changes according to the rotation angles of the plurality of orthogonal mirrors. Generating a polarization mode dispersion stress. A light incident part (21) for causing an optical signal to be given polarization mode dispersion to be incident;
Polarization separation means (22, 23) for separating the optical signal incident on the light incident portion into two orthogonal polarization components;
First delay means (25) for receiving one of the two orthogonally polarized components, passing through the first optical path, and emitting with a delay corresponding to the length of the first optical path;
Second delay means (26) for receiving the other of the two orthogonally polarized components, passing through the second optical path, and emitting with a delay corresponding to the length of the second optical path;
Polarization multiplexing means (22, 28) for combining one orthogonal polarization component delayed by the first delay means and the other orthogonal polarization component delayed by the second delay means;
A light emitting section (29) for emitting the light combined by the polarization multiplexing means to the outside,
At least one of the first delay means and the second delay means is:
A plurality of orthogonal mirrors (50) that receive and fold the polarization-separated light separately in the width direction, and the plurality of orthogonal mirrors are parallel to a boundary line where a pair of orthogonal reflecting surfaces forming the orthogonal mirror intersect. A rotation device (52) that rotates integrally with a shaft, and propagates while varying a delay time difference imparted to each light component folded by each orthogonal mirror, and the polarization multiplexing means A polarization mode dispersion stress generating apparatus, characterized in that a group delay time difference of polarization components of combined light is changed according to rotation angles of the plurality of orthogonal mirrors. A single polarization beam splitter (22) serves as both the polarization separation means and the polarization multiplexing means,
Quarter wavelength plates (31, 32) are inserted between the polarization beam splitter and the first delay means and between the polarization beam splitter and the second delay means, respectively.
The first delay means and the second delay means receive the orthogonal polarization components separated by the polarization beam splitter through the quarter wavelength plates, and fold them in the opposite directions around the same optical axis, and again Incident light into a quarter-wave plate, converted into orthogonal polarization components whose polarization directions are 90 degrees different from those at the time of separation, and returned to the polarization beam splitter with the same optical axis as that at the time of separation, 3. The polarization mode dispersion stress generating apparatus according to claim 2, wherein the light is emitted along an optical axis orthogonal to an incident optical axis of the optical signal to the polarization beam splitter.   3. The polarization mode dispersion stress generating apparatus according to claim 2, wherein the polarization beam splitting unit and the polarization beam combining unit are configured by individual polarization beam splitters (23, 28), respectively.   The beam expander (53) for expanding the beam width of light incident on the plurality of orthogonal mirrors is disposed between the polarization separating means and the plurality of orthogonal mirrors. The polarization mode dispersion stress generator according to any one of the above. The light incident part is provided with a collimator (21b) that widens the beam width of incident light to make parallel light, and the light emitting part is provided with a condenser lens (29a) for condensing the combined light. And
The collimator of the light incident part and the condensing lens of the light emission part are respectively formed by two sets of cylindrical lenses whose beam width expansion directions are orthogonal to each other. The polarization mode dispersion stress generator as described.   The polarization mode dispersion stress according to any one of claims 2 to 5, wherein a polarization scrambler (21c) for randomizing a polarization state of incident light is provided in the light incident portion. Generator. A branching device (56) for branching a part of the light combined by the polarization multiplexing unit and output to the light output unit;
An analyzer (57) having a polarization axis inclined by 45 degrees with respect to both polarization directions so as to extract both polarization components from the light branched by the splitter;
A light receiver (58) for receiving both polarization components detected by the analyzer;
The light reflection means (25a) included in at least one of the first delay means and the second delay means is slid in a direction parallel to the incident optical axis, and the optical path length turned back by the light reflection means is uniformly changed. Slide driving means (25b)
The first delay means based on the output of the light receiver when the slide driving means is controlled in a state where a broadband light source is incident from the light incident portion and the angles of the plurality of mirrors are fixed to a predetermined angle. The polarization direction according to any one of claims 2 to 6, wherein the optical path lengths of the second delay means and the second delay means are adjusted, and the plurality of mirrors are rotated from the predetermined angle from a state in which the optical path lengths are matched. Mode distributed stress generator.

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